Conversion of Aluminum Phosphate to Sodium Phosphate

Home , Phosphoric acid

Journal of Materials Science and Engineering A 6 (11-12) (2016) 321-325 doi: 10.17265/2161-6213/2016.11-12.005 D DAVID PUBLISHING

Masaaki Takahashi1*, Yukimasa Takemoto1, Maki Ooyagi1, Ken Oonishi2 and Eiji Yuuki2 1. Yokkaichi University, Research Laboratory on Environmental Technology, Kayo-cho 1200, Yokkaichi, Mie, 512-8512, Japan 2. Mie Chuo Kaihatsu Co., Ltd, Hachiya4713, Yono, Iga, Mie, 518-1152, Japan

Abstract: The phosphorus recovered from sewage sludge by acidic treatment is mainly composed of aluminum phosphate. To make a wide utilization of recovered phosphorus, removal of the aluminum component is considered a very important matter. In order to find a method to convert aluminum phosphate to sodium phosphate, a basic investigation was carried out. A reagent of aluminum phosphate was dissolved by aqueous solution of sodium hydroxide, and mixed with sodium silicate to make a alunino-silicate gel. Sodium phosphate was recovered from residue water in the gel.

Key words: Aluminum phosphate, sodium phosphate, gelation, sodium silicate.

1. Introduction where M is alkali metal, m, n, x, y and z are indefinite numbers. Sewage sludge contains significant amounts of In order to confirm this method, we investigated the phosphorus, and in order to recover the phosphorus, reaction using a reagent of sodium hydroxide, some studies have been carried out [1-6]. The aluminum phosphate and sodium silicate. phosphorus which is recovered by acidic treatment contains a lot of aluminum [7]. To make a wide 2. Method utilization of recovered phosphorus, the removal of 2.1 Preparation the aluminum component is considered a very important matter, and some methods were investigated In this experiment, sodium hydroxide: Kanto [8]. chemical Co., INC (assay minimum 97%), aluminum The aluminum component in the recovered phosphate: Kanto chemical Co., INC (assay minimum phosphorus is considered to exist mainly as a form of 95 % as AlPO4), sodium silicate: Kanto chemical Co., aluminum phosphate. Aluminum ion reacts with alkali INC (assay minimum SiO2: 37%, Na2O: 18%) was metal silicate to form a silicate gel, which is widely used. known as zeolite synthesis. Aluminum phosphate is Aqueous solutions of these reagents were prepared dissolved by the addition of aqueous solution of alkali as mentioned below: metal hydroxide, and is also expected to react with Aq. aluminum phosphate solution: 50 g of alkali metal silicate to make an alkali metal silicate aluminum phosphate was resolved by addition of 50 g gel. Using this reaction, alkali metal phosphate is of sodium hydroxide in 1,000 mL of water. considered to be recovered as reaction (1) [9]. Aq. sodium silicate solution: 100 g of sodium silicate was in 100 mL of water (total volume 155 MSiO23 mAlPO 4 nMOH (1) mL). MOxAlO2232234  ySiO  zHO  MPO 2.2 Experimental Procedure *Corresponding author: Masaaki Takahashi, researcher, research field: environmental technology. The experiment was carried out as shown in Fig. 1.

322 Conversion of Aluminum Phosphate to Sodium Phosphate

Aq. aluminum phosphate solution

Aq. sodium silicate solution

Extract Solution Gelation Frieze, de-freezing Separation Evaporation

Residue

Gel Phosphorus

Fig. 1 Experimental procedure.

Aq. sodium silicate solution was added to the aq. of pH 11.5. The formed gel was cooled in an ice box, solution of aluminum phosphate at room temperature and dehydration was carried out as mentioned before. and the mixture formed a transparent gel. In order to The dehydrated gel was dried and the phosphorus estimate the amount of the gel, dehydration is needed. containing extract was evaporated for analysis, and gel To make rapid dehydration, a freezing and de-freezing (17 g) and phosphorus, (23 g) were recovered. method applied to the dehydration of sludge [10], was 3. Result and Discussion carried out. The formed gel was cooled in an ice box (under -10 ºC) for one day, later, the frozen gel was 3.1 Addition Rate retained at a room temperature (about 25 ºC) to make The relation of the amount of the formed gel and de-freezing. The dehydration was brought about the addition rate of the sodium silicate is shown in through de-freezing, and the dehydrated gel was Fig. 2. The amount of the formed gel, increased by separated by filtration, and the residue was dried at addition of sodium silicate, and when the addition rate 105 ºC for analysis. The phosphorus component was reached 10g, amount of the gel tends to plateau. This recovered from the extract through evaporation. addition rate is considered to correspond to a

2.3 Addition Rate molecular ratio Al2O3 : SiO2 = 0.35 : 1.

In order to find a proper addition rate, 5 mL to 20 3.2 Properties of Recovered Materials mL of aq. sodium silicate solution was added to 100 The recovered gel is a white powder, particle size: mL of aq. aluminum phosphate solution at room under 0.05 mm as shown in Fig. 3, bulk density: temperature (about 25 ºC), and the mixture formed a 0.2~0.3 g/cm3. The chemical component of the gel in a few minutes. The formed gel was cooled in an recovered gel and phosphorus was analyzed by X-ray ice box for 24 hours, and the frozen gel was retained in a room for de-freezing. Dehydration took place Gel (g) through de-freezing, and the dehydrated gel was 8 7 separated using filter paper (ADVANTEC, No2, Toyo 6 Roshi Co LTD), and residue (gel) was dried at 105 ºC 5 4 for analysis. 3 2 2.4 Recovery of Phosphorus 1 0 A 200 mL of aq. aluminum phosphate solution was 0 5 10 15 mixed with a 30 mL of aq. sodium silicate solution at Sodium silicate (g) room temperature, and a gel was formed in a condition Fig. 2 Relation of sodium silicate and formed gel.

Conversion of Aluminum Phosphate to Sodium Phosphate 323

chemical composition of the raw material was calculated by mass balance of the reagent used in this experiment. The recovered gel was composed

of Na2O、SiO2、Al2O3, and it was considered to be a compound of alumino- silicate. The elemental ratio of the gel was calculated from the analyzed data and the approximate molecular ratio was considered as (2).

Na2O·xAl2O3·ySiO2; x/y = 1/ 3 (2) The ratio of x : y corresponds to the chemical composition of a zeolite [11]. However, XRD of the gel shows the pattern of an amorphous compound Fig. 3 Photo of the gel. (Fig. 5), and further investigation is needed to identify

some properties and physical structure. 100% The amount of P2O5 component in the gel is small, 80% others 60% and almost of all the phosphorus was separated from P2O5 40% the gel as an extract. The recovered phosphorus was Al2O3 20% Na2O composed of P2O5 and Na2O, and is considered to be a 0% form of Na2HPO4·7H2O by the XRD analysis (Fig. 6) Raw Gel Crystal SiO2 material and recovered condition (pH11-pH12) [12].

A small amount of SiO2 component was found in Fig. 4 Chemical composition of recovered materials. the recovered phosphorus, which is considered analyzer, (XRF, Rigaku Corporation SPECTRO non-reacted sodium silicate which remained in the XEPOS) and the result is shown in Fig. 4. The recovered phosphorus.

Counts

Fig. 5 XRD spectrum of the gel.

324 Conversion of Aluminum Phosphate to Sodium Phosphate

Counts

Na2HPO4

Na2HPO4 7H2O

Na2SiO3 9H2O

Na2SiO3 5H2O

Fig. 6 XRD spectrum of the recovered crystal.

4. Conclusions Ohtake, H. and Miura, K. et al. 2013. “Novel Technique for Phosphorus Recovery from Aqueous Solutions Using In order to find a wide utilization of aluminum Amorphous Calcium Silicate Hydrates (A-CSHs).” Water phosphate which is recovered from sewage sludge, a Research 47 (7): 2251-9. [3] Nakahara, K. 2001. “Vitrification Process for Recovery conversion method of aluminum phosphate to sodium of Phosphorus/Phosphoric Acid from Sewage Sludge phosphate was investigated using a reagent of Ash.” Industrial Water 514: 2-10. aluminum phosphate. Aluminum phosphate which [4] Sonoda, K., Tokukura, K., Mori, T., Komazawa, I. and was dissolved by sodium hydroxide reacted with Wada, T. 1996. “Phosphoric Acid Recovering from Incinerated Ashes of Sewage Treatment Sludge.” In sodium silicate, and formed a silicate gel. Aluminum Proceedings of the 7th Annual Conference of the Japan phosphate was converted to sodium phosphate Society of Waste Management Expert, 267-9. through the formation of alumino-silicate gel. The [5] Ingham, J., Ryan, J., Keyakida, E. and Ri, J. 1996. “Phosphorus and Metal Recovery from Sewage result indicates a possibility to make a recovery Treatment Sludge.” In Proceedings of the 7th Annual method of sodium phosphate from sewage sludge. Conference of the Japan Society of Waste Management However, further study is needed to investigate the Expert, 280-2. conversion of sodium phosphate from aluminum [6] Yoshida, K., Takahashi, Y. and Hatano, M. 2001. “The Experiment on the Recovering pf Sodium Phosphate from phosphate which is recovered from sewage sludge. Incinerated Ash of Sewage Sludge.” In Proceedings of Reference the 12th Annual Conference of the Japan Society of Waste Management Expert, 280-2. [1] Shima, H. and Takahashi, M. 1997. Gekkan [Mizu] [7] Takahashi, M., Takemoto, Y. and Oonishi, K. 2013. Publishing, Gekkan Water (In Japanese). 39-7 (552): “Recovery of Aluminum Phosphate Using Magnesium 36-40. hydroxide from Incinerated Ash of Sewage Sludge.” [2] Okano, K., Umemoto, M., Kagami, J., Honda, K., Journal of Material Science and Engineering A 3 (10):

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